Allow farm output to be boosted by gasoline

[Talus]

Note:
This does not address any specific problem, but is a potentially new game mechanic influenced by the gas price & farming crisis happening in many parts of the real world.

Proposal:
Farm output is increased by some percent by consuming gasoline. If a nation runs out of gasoline, then farm output will be reduced to some minimal level.

Impact:
* Gasoline is not used during peace time and this would make the resource important through war/peace cycles.
* Depending on how much gas farms would consume and the cost of gas, producing food could potentially become less profitable unless the price of food increases.

As for tuning the mechanic, we could either have base farm output remain at current levels with gasoline giving some productivity boost or if we don't want to increase the availability of food then we could reduce farm output unless farms are supported with gasoline.

[Federative Woodstock]

Nitpick: Gasoline resource reserves don't designate the civilian access to gasoline. It's more or less a wartime military reserve.